This invention pertains to a method of reducing the consistency of a stucco slurry.
Gypsum wallboard is a large volume product in the United States where it is used for interior walls in most new construction. Low cost, wide availability, the safety its fire retarding nature imparts to the finished structure, and ease of use contribute to its popularity.
For a brief explanation of the uses, properties, and production methods of gypsum and stucco, Volume 4 of Kirk-Othmer's "Encyclopedia of Chemical Technology" (1978 ed.) at pages 437-448 may be consulted.
The production of gypsum wallboard is uncomplicated. Various commercial methods of producing gypsum board are well-known in the art. Gypsum, the dihydrate of calcium sulfate, is mined, ground, and calcined to give the hemihydrate known commonly as stucco or plaster of Paris. In a mixer, stucco, water, and additives are combined to form a stucco slurry. The stucco slurry is fed between two continuous sheets of paper to form a board on a conveyor. While the board moves down the conveyor, the stucco sets to reform gypsum, the dihydrate.
A workable stucco slurry requires more water than is needed to reform the dihydrate. After setting, the excess water must be driven off to produce the finished wallboard. Typically, drying kilns are used to remove the excess water. Since drying kilns are energy intensive, a major cost in wallboard production would be lessened if the amount of excess water in the stucco slurries was reduced.
Currently, lignosulfonates and napthalene sulfonates are used as consistency reducers to minimize the amount of water needed in a stucco slurry. However, the sulfonates' tendency to significantly retard set time limits their level of use.
Therefore, it would be advantageous to the gypsum wallboard industry to possess additives which reduce a stucco slurry's consistency without significantly retarding set time. The gypsum wallboard industry would benefit from such additives because the additive would reduce the energy costs spent to drive off the excess water in drying kilns and thereby produce the finished wallboard. And moreover, it would be beneficial if the additive would do so without significantly retarding set time.